This invention relates generally to an automatic control system for a dynamically deflectable head in a video tape recorder, and is particularly directed to an automatic control system for adjusting the head height during recording of signals by means of such a video tape recorder.
Helical scan video tape recorders are required to reproduce recorded video signals in non-standard modes, such as, still, slow, reverse, and fast motion modes, in addition to the normal playback mode. Such non-standard modes are established by changing the tape transport speed and/or direction. When the tape transport speed during reproduction is the same as that during recording, the slant angle at which the reproducing heads scan the tape is equal to the slant angle of the previously recorded tracks.
The same is not true when the tape transport speed or direction used during reproduction differs from the speed or direction, respectively, used for recording. Instead, due to the tape transport speeds or directions at recording and reproduction being different, the path of the head used for reproducing deviates angularly from the recorded tracks. In order to avoid scanning by the reproducing head of two or more recorded tracks, and the generation of guard-band noise, and the like, so-called dynamic tracking is employed in which the reproducing head is mounted on an electrically deflectable element, such as a bi-morph leaf, to which a properly timed and shaped electrical signal is applied during each scan. In response to such electrical signal, the bi-morph leaf deflects and maintains the path of the reproducing head along a selected track during the scan.
However, a bi-morph leaf is subject to hysteresis, that is, once it is electrically deflected by an electrical signal, mere removal of the electrical signal may not cause the bi-morph leaf to return to its original condition. Instead, a residual deflection or distortion may remain in the bi-morph leaf. This residual distortion can be relatively large when the preceding electrical deflection has been large, as may be required for dynamic tracking during fast, slow and still reproduction.
If the head mounted on a bi-morph leaf which retains a residual deflection or distortion is used for recording, the recorded tracks produced by such head are located at different positions from the normal tracks, and the pitch of the recorded tracks may be non-uniform.
As a consequence, the prior art has employed separate heads for reproduction and recording with only the reproducing head being mounted on a bi-morph leaf for dynamic tracking, and with the recording head being fixed. Such provision of separate heads for recording and reproducing increases the cost of a VTR.